1. Field of Invention
The invention relates to an alkaline storage battery.
2. Description of Related Art
In recent years, various alkaline storage batteries have been developed. For example, Japanese Patent Application Publication No. JP-A-2001-313066 discloses an alkaline storage battery in which an electrode body formed by alternately stacking a plurality of positive plates and a plurality of negative plates with one separator disposed between every two plates is housed in a rectangular parallelepiped-shape battery case. This alkaline storage battery has electrode terminals (a positive terminal and a negative terminal) that are disposed astride the inside and the outside of the case through penetration holes penetrating a lid of the case.
In the alkaline storage batteries, due to the use of an alkaline electrolyte, a so-called electrolyte solution creep phenomenon occurs in which the electrolyte solution in the case creeps up the surfaces of the electrode terminals. This phenomenon is remarkable particularly in the negative terminal. Therefore, in the alkaline storage battery shown in Japanese Patent Application Publication No. JP-A-2001-313066, if the sealing of a penetration hole in which an electrode terminal is inserted is not sufficient, the electrolyte solution may leak out along the surfaces of the electrode terminals after a long time of use due to the creep phenomenon of the electrolyte solution.
Japanese Patent Application Publication No. JP-A-2003-272589 discloses a closed-type alkaline storage battery that has good seal characteristic, and restrains the seepage of the electrolyte solution from inside the battery, and operates a safety valve appropriately. In this closed type alkaline storage battery, in order to prevent leakage of the electrolyte solution via the safety valve, a surface roughness Ra is prescribed regarding a region in an opening closure plate which contacts a protection portion of the valve body. However, the surface roughness Ra, being an representation of an arithmetic average from an average line of a roughness curve, is not suitable to prescribe the surface roughness of a seal portion of an electrode terminal (a site that prevents the alkaline electrolyte from leaking out along the surfaces of the electrode terminal) that has undergone complicated forming (deep draw molding or the like). A reason therefor is that an electrode terminal having undergone complicated molding (deep draw molding or the like) may sometimes have local roughening of the surface of the seal portion to great extent due to occurrence of cracks and the like, and in such a case, the alkaline electrolyte may leak out via a site where cracks or the like occur, even if the value of Ra is small.